Paraelectric Phase Transition Research Articles

Structure and Electrical Properties of Sr1.85Ca0.15NaNb5O15 Ceramics with Addition of Multivalence Oxides (MnO2, PbO2)

Sr1.85Ca0.15NaNb5O15 (SCNN15) ceramics with different additions of MnO2 and PbO2 have been prepared by the conventional solid-state reaction method and their phase structure, microstructure, and dielectric and ferroelectric properties investigated. X-ray diffraction results showed that the single tungsten bronze structure of SCNN15 was not changed by adding MnO2 and PbO2. X-ray photoelectron spectroscopy results demonstrated that Mn and Pb ions were both present in mixed valence of +2 and +4. It was also found that the two kinds of dopant had remarkable effects on the dielectric and ferroelectric properties of the SCNN15 ceramic. The dielectric spectra of all specimens showed two broad dielectric anomalies: one diffuse high-temperature anomaly, caused by the ferroelectric (4mm) to paraelectric (4/mmm) phase transition at the Curie temperature (T C), and a relaxor low-temperature anomaly, associated with the ferroelectric (mm2) to ferroelectric (4mm) phase transition at lower temperature (T s). The electrical performance of SCNN15-0.10 wt.% MnO2 and SCNN15-0.10 wt.% PbO2 ceramics was comprehensively investigated. Moreover, the underlying mechanism for the variation of the electrical properties for the different dopants is explained.

Structural and dielectric properties of Pb(1−x)(Na0.5Sm0.5) x TiO3 ceramics

A correlation between structure and vibrational properties related to a ferroelectric to paraelectric phase transition in perovskite Pb(1−x)(Na0.5Sm0.5) x TiO3 (0 ≤ x ≤ 0.5) (PNST-x) polycrystalline powders is discussed. Substitution leads to reduction of tetragonality which is associated with a shift of the phase transition to lower temperatures. The nature of the phase transition gets diffused with increasing substitution.

Piezoelectric and ferroelectric properties of lead-free (1-x)(Na1−yKy)(Nb1−zSbz)O3-xBaTiO3 solid solution

The solid solutions of lead-free (1-x)(Na1-yKy)(Nb1-zSbz)O3-xBaTiO3 (with x=0.1, 0.2; y=0.03, 0.05; z=0.05, 0.1) (abbreviated as (1-x)NKNS-xBT) ceramics have been synthesized using conventional solid-state reaction method. The results of X-ray diffraction analysis show that all the grown specimens of NKNS display typical perovskite structure. With BaTiO3 (BT) addition, a structural phase transition from tetragonal to cubic structure has been observed. The structural parameters of (1-x)NKNS-xBT powders were determined by profile refinements based on the analysis of X-ray powder diffraction. The charge density distributions of the prepared samples have been investigated by observed structure factors to understand the chemical bonding nature of (1-x)NKNS-xBT powders. The optical absorption of the ceramics has been investigated using UV–visible spectrophotometer. Scanning electron microscopic (SEM) measurements were performed to study the surface morphology of the prepared solid solutions. The elemental compositions of the (1-x)NKNS-xBT samples were analyzed by energy-dispersive X-ray (EDS) spectrometer. The dielectric constant versus temperature plots of the solid solutions exhibit ferroelectric to paraelectric phase transition, which is dependent on the BaTiO3 content. The ferroelectric nature of the samples has been determined through polarization and electric field hysteresis measurements.

Effects of Sn doping on the microstructure and dielectric and ferroelectric properties of Ba(Zr0.2Ti0.8)O3 ceramics

Ba(Zr0.2Ti0.8)1−x Sn x O3 ceramics are prepared via the conventional solid state reaction method. The effects of Sn doping on microstructure, dielectric and ferroelectric properties of Ba(Zr0.2Ti0.8)1−x Sn x O3 ceramics were investigated. These results indicate that Sn4+ ions enter the unit cell maintaining the perovskite structure of solid solution and substitute preferentially for Zr4+ and then Ti4+ when Sn content (x) gradually increases from 0 to 0.2. Introduction of Sn4+ on B sites makes grain more uniform and regular. The addition of Sn4+ results in the fall of the Curie temperature. The temperature dependences of dielectric properties of Ba(Zr0.2Ti0.8)1−x Sn x O3 ceramics indicate that the addition of stannum leads to the enhancement of the diffuseness of ferroelectric–paraelectric phase transition. Moreover, it can be found that the ferroelectric properties deteriorate as Sn content increases.

Ferroelectric phase transition and electrical conduction mechanisms in high Curie-temperature PMN-PHT piezoelectric ceramics

Ferroelectric phase transition characteristic and electrical conduction mechanism of the high Curie-point (TC) 0.15Pb(Mg1/3Nb2/3)O3−0.4PbHfO3−0.45PbTiO3 (PMN-PHT) piezoelectric ceramics were studied by the temperature dependent Raman spectra and electrical properties. Sole first-order ferroelectric phase transition is demonstrated by the thermal hysteresis behavior of the temperature dependent dielectric constant and the dramatic drop of the derivative of inverse dielectric constant ξ= d(1/εr)/dT around TC in the PMN-PHT ceramics. The temperature dependent Raman spectroscopy not only provides further evidence for the ferroelectric to paraelectric phase transition appearing around TC in the PMN-PHT ceramics, but also reveals the successive phase symmetry changes of the polar nanoregions (PNRs), in which apparent anomalies appear in the Raman peaks' wavenumber, wavenumber distance, intensity, intensity ratio, and line width of some selected Raman modes upon heating. Typical sole cole-cole circle is obtained for the PMN-PHT ceramics in the temperature range of 440–560°C, based on which the activation energy (Ea) of the electrical conduction is calculated being ~1.2eV. Such low value of Ea indicates that the oxygen vacancies formed in the PHT-PMN ceramics induced by the evaporation of Pb during the sintering process dominate the high-temperature extrinsic electrical conduction.

Preparation and characterization of Bi4–xPrxTi3O12 solid solutions

The Bi4–xPrxTi3O12 (BPT) solid solutions (x = 0.05, 0.10, 0.15) with small praseodymium content were prepared by solid-state method. Thermal, electric, and dielectric properties of BPT were studied. It was revealed that BPT titanates crystalize in аn orthorhombic structure and exhibit p-type semiconductivity. Dielectric constant of BPT increased, Curie temperature (TC), electrical conductivity and dielectric losses decreased, but lattice parameters and thermo-EMF coefficient remained practically unchanged with the increase of praseodymium content in layered Bi4–xPrxTi3O12. It was determined that activation energy of direct current (DC) electrical conductivity and linear thermal expansion coefficient (LTEC) of BPT changes at ferroelectric (FE) → paraelectric (PE) phase transition. The activation energy and LTEC changed below and above TC from 1.08–1.56 eV to 0.45–0.86 eV and from (9.10–10.80)×10–6 K–1 to (13.12-14.61)×10–6 K–1, respectively. The AC electrical conductivity studies of BPT illustrated short-range order with ionic translations assisted by small-polaron hopping.

Two novel metal–organic coordination polymers based on ligand 1,4-diazabicyclo[2.2.2]octane N,N′-dioxide with phase transition, and ferroelectric and dielectric properties

The synthesis of two low-temperature structural phase transition compounds {[Ag3(dabcodo)(NO3)3]·H2O}n (1) and [Ca(Dabcodo)(H2O)4Cl2]n (2) are described. Compound 1 displayed ferroelectric–ferroelectric phase transition.

Synthesis of Barium Titanate Using Deep Eutectic Solvents.

Novel synthetic routes to prepare functional oxides at lower temperatures are an increasingly important area of research. Many of these synthetic routes, however, use water as the solvent and rely on dissolution of the precursors, precluding their use with, for example, titanates. Here we present a low-cost solvent system as a means to rapidly create phase-pure ferroelectric barium titanate using a choline chloride-malonic acid deep eutectic solvent. This solvent is compatible with alkoxide precursors and allows for the rapid synthesis of nanoscale barium titanate powders at 950 °C. The phase and morphology were determined, along with investigation of the synthetic pathway, with the reaction proceeding via BaCl2 and TiO2 intermediates. The powders were also used to create sintered ceramics, which exhibit a permittivity maximum corresponding to a tetragonal-cubic transition at 112 °C, as opposed to the more conventional temperature of ∼120 °C. The lower-than-expected value for the ferro- to para-electric phase transition is likely due to undetectable levels of contaminants.

The influence of the crystallization temperature on the reliability of PbTiO3 thin films prepared by chemical solution deposition

The preparation of quality ferroelectric PbTiO3 (PT) thin films at the lowest possible temperature preserving its functional properties is necessary for their integration in microdevices. The crystallization below, close or above the para-ferrolectric transition temperature of the PbTiO3 must produce an important effect on the microstructure, texture and residual stress state of the films and on functional properties. In this paper, the Chemical Solution Deposition method has been used to prepare PbTiO3 films at different temperatures around that of the ferroelectric to paraelectric phase transition. The films were analyzed by X-ray diffraction, Optical and Scanning Electron Microscopy, and their microstructure, texture and residual stress correlated with their functional properties. The results show that these PT films prepared with crystallization temperatures close or below the phase transition develop a favorable microstructure and texture that lead to high remnant and saturation polarization values, making them good candidates for their integration in microdevices.

Sol-hydrothermal synthesis, crystal structures and excellent dielectric stability of yttrium doped BaTiO3 ceramics

Monodisperse Yttrium-doped BaTiO3 (YBT) nanoparticles with good crystallinity and uniform size distribution have been synthesised via a modified sol-hydrothermal method. The solubility of yttrium in BT was no more than 1 mol%. However, at higher Y3+ content, excess Y3+ were inclined to form Y(OH)3 impurities, and after high temperature sintering, impurity YBa3Ti2O8.5 can be detected in the ceramics. Further, the variation in the crystal volume indicated that Y3+ preferred to substitute for Ti4+ as an acceptor. FE-SEM images revealed that the grain size of the ceramics gradually decreased with the raising Y3+ concentration. Notably, YBT ceramics with 3 mol% Y3+ presented outstanding dielectric-temperature stability, benefitting from the diffuse ferroelectric–paraelectric phase transition and the existence of YBa3Ti2O8.5 phases. Stable dielectric-temperature property and low dielectric loss of the YBT ceramics doping with 3 mol% Y3+ in the range from 1 kHz to 1 MHz render it as a promising candidate material for high frequency application.

Structural and Electrical Properties of Na2Pb2Dy2W2Ti4Ta4O30 Ceramic

The structural, ferroelectric, and electrical properties of tungsten bronze Na2Pb2Dy2W2Ti4Ta4O30 ceramic, synthesized by a standard high-temperature solid-state reaction route, have been studied. Formation of a single-phase orthorhombic crystal system was verified by x-ray diffraction analysis. Microstructural analysis of a pellet sample by scanning electron microscopy revealed well-defined grains of almost the same dimension, uniformly distributed on the surface. Detailed studies of the dielectric properties of the compound as a function of frequency and temperature showed that the compound undergoes a ferroelectric–paraelectric phase transition of diffuse type. The frequency dependence of the alternating-current (ac) conductivity showed the signature of Jonscher’s universal power law. Conductivity study over a wide temperature range suggested that the compound exhibits negative temperature coefficient of resistance behavior.

Magnetoelectric effect in lead free piezoelectric Bi1/2Na1/2TiO3–modified CFO based magnetostrictive (Co0.6Zn0.4Fe1.7 Mn0.3O4) particulate nanocomposite prepared by sol-gel method

Lead free magnetoelectric composites that comprise Co0.6Zn0.4Fe1.7Mn0.3O4 (CZFMO) and Bi1/2Na1/2TiO3 (BNT) were synthesized using sol-gel method and it's structural, dielectric, magnetic, ferroelectric and magnetoelectric (ME) properties were studied. The X-ray diffraction displayed the single phase formation of parent phases and the presence of two phases in the composites. The temperature dependent dielectric spectra of samples indicates two anomalies at ~220°C and ~320°C were ascribed to ferroelectric to antiferroelectric, and anti-ferroelectric to paraelectric phase transitions respectively. Room temperature (RT) magnetic measurements show that composites are soft magnetic. The composite with x=0.2, showed the large value of ME voltage coefficient (αE)~58mV/cmOe. Moreover, these ME composites provide a great opportunity as potential lead free systems for multifunctional devices.

Dielectric Property Conduction Mechanism and Thermal Analysis of Cu 1 . 0 9 Ni 0 . 9 1 (HSeO3)2Cl2⋅4H2O Compound

The Cu1.09Ni0.91(HSeO3)2Cl2⋅4H2O (noted CuNiSe) compound was prepared from an aqueous solution reaction and crystallizes in the orthorhombic Pnma space group. It was analyzed by single-crystal X-ray diffraction and the X-ray powder diffraction to confirm the purity of the synthesized compound. The structure of this compound consists by a three-dimensional framework structure, constructed by layers parallel to the (010) plane formed by copper/nickel octahedral and (HSeO\(_{3}^{\mathrm {-}})\) trigonal pyramids. The thermal analysis of the CuNiSe compound shows three endothermic peaks at 410, 433, and 473 K. The Raman spectra of CuNiSe have been recorded from 299 to 479 K. In addition, the dielectric evolution constant as a function of frequency and temperature revealed a ferroelectric–paraelectric phase transition about 433 K and superprotonic phase transition about 473 K. However, the conductivity evolution versus temperature confirmed the presence of these two types of phase transitions.

The novel dielectric relaxation behavior around the Curie point of (Ba0.7Sr0.3)0.96Y0.04TiO3 ceramics with giant effective permittivity

The temperature (80 K ∼ 423 K) and frequency (40 Hz ∼ 5 MHz) dependence of the permittivity were studied in (Ba0.7Sr0.3)0.96Y0.04TiO3 ceramics. A giant effective permittivity over 105 with a certain frequency and temperature stability and Debye-type dielectric relaxation behavior was observed. The complex impedance spectrum analysis reveals that the giant permittivity is due to the heterogeneous structure with a semiconducting bulk and high resistance electrode–ceramic interface. Deviating from low temperature (below 200 K) thermal activated behavior, the odd change of the characteristic relaxation frequency around the Curie point is observed and proven to be induced by the competition between the positive temperature coefficient of the resistance effect of the bulk ceramic and the dielectric anomaly of the surface layer capacitance, both of which originate from the ferroelectric–paraelectric phase transition.

Evolutions of stress and microstructure in multilayer ferroelectric actuators under different temperature environments

ABSTRACTThe multilayer ferroelectric actuator (MFA) with electrodes is an important smart structure and it has found wide application in engineering. Under the applied electric–elastic loads, the local stress concentration will be intensified near the tips of electrodes, and it finally may lead to the failure of the MFA. On the other hand, the temperature-dependent behavior of ferroelectrics results in the novel evolutions of local stresses and microstructure in the MFA under different temperature environments. In this work, the different temperature-induced nonlinear behavior and electroelastic field concentration around the electrode tip in the MFA is studied based on a phase-field approach containing the time-dependent Ginzburg–Landau equation. Using three-dimensional nonlinear finite element method, the temperature-induced domain switching behavior of the MFA and the evolution of the local stress near the electrode tips are simulated under different loadings and temperatures. It is found that the maximum tensile stress ahead of the electrode tip increases as the temperature increases from room temperature to a critical temperature. However, over the critical temperature, the stress decreases significantly due to the ferroelectric–paraelectric phase transition, which implies that by optimizing the environmental temperature, the local stress concentrations can be controlled.

Ferroelectric phase transitions of the 0.32PIN-0.345PMN-0.335PT single crystals studied by temperature-dependent Raman spectroscopy, dielectric and ferroelectric performance

ABSTRACTThe ferroelectric phase transition characteristics of the 0.32Pb(In1/2Nb1/2)O3-0.345Pb(Mg1/3Nb2/3)O3-0.335PbTiO3 (0.32PIN-0.345PMN-0.335PT) single crystals were studied by the temperature-dependent Raman spectroscopy and some electrical properties. Ferroelectric monoclinic phase was confirmed at room temperature by the numbers of the Raman modes. Successive ferroelectric phase transitions, i.e. ferroelectric monoclinic phase to ferroelectric tetragonal phase transition (FEM-FET) and ferroelectric tetragonal phase to paraelectric cubic phase transition (FET-PC), are evidenced by the anomalies of Raman modes line width, peaks intensity and their ratios around TM-T and TC/Tm temperatures. The temperature dependent permittivity derivative ξ = dϵ/dT not only provides further evidence of the successive ferroelectric phase transitions, but also demonstrates the second-order transition characteristic of the FEM-FET phase transition and the first-order transition feature of the FET-PC phase transition. The FEM-FET phase transition is also confirmed by the abnormal narrowing of the P-E loops, decrease of the Pr and Ec values, and extremums of the pyroelectric performance.

A comparative study on structural, dielectric and multiferroic properties of CaFe2O4/BaTiO3 core-shell and mixed composites

The core-shell CaFe2O4@BaTiO3 and (1−x) CaFe2O4 - xBaTO3 (x = 0.3, 0.5, 0.7) mixed composites were synthesized using a combination of solution processing and solid state reaction method respectively followed by high temperature calcinations. The presence of the constituent spinel-ferrite phases in both core-shell and mixed nanocomposites were confirmed by X-ray diffraction patterns and transmission electron microscopy. High-resolution transmission electron microscope images indicate a clear view of ferrite and ferroelectric phases in each core-shell and mixed composite, where the ME coupling effect of ferrite and ferroelectric phase happened. Dependence of dielectric constant (ε′), loss tangent (tan δ) and AC conductivity (σAC) with frequency (100 Hz–2 MHz) and temperature (25 °C–550 °C) with increasing probing frequency (1 kHz–2 MHz) of the composites have been investigated. The peak observed in mixed composites and core-shell nanostructures in the low temperature range (130 °C–150 °C) are attributed to ferroelectric to paraelectric phase transition of BaTO3. The second peak observed at high temperature attributed to TC (Curie temperature) of the ferrite (CaFe2O4) phase. The core-shell composite did not show any magnificent improvement in dielectric properties than mixed composites. The presence of ordered FE and FM behavior at room temperature was confirmed by observation of P-E and M-H hysteresis loops; respectively and core-shell composite shows drastic improvement in ferroelectric, magnetic and magneto-electric properties than the mixed composites. In addition, the calculated linear ME coupling coefficient results reveal strong ME coupling effect and the maximum recorded value is ∼30.32 mV/cmOe for the core-shell composite. The larger value of ME coupling coefficient may arise from larger saturation magnetization and remnant magnetization of the core-shell composite.

Preparation and Characterization of BaTiO3–PbZrTiO3 Coating for Pyroelectric Energy Harvesting

Harvesting energy from waste heat is a promising field of research as there are significant energy recovery opportunities from various waste thermal energy sources. The present study reports pyroelectric energy harvesting using thick film prepared from a (x)BaTiO3–(1 − x)PbZr0.52Ti0.48O3 (BT–PZT) solid solution. The developed BT–PZT system is engineered to tune the ferro to paraelectric phase transition temperature of it in-between the phase transition temperature of BaTiO3 (393 K) and PbZrTiO3 (573 K) with higher pyroelectric figure-of-merit (FOM). The temperature-dependent dielectric behavior of the material has revealed the ferro- to paraelectric phase transition at 427 K with a maximum dielectric constant of 755. The room-temperature (298 K) pyroelectric coefficient (Pi) of the material was obtained as 738.63 μC/m2K which has yielded a significantly high FOM of 1745.8 J m−3 K−2. The enhancement in pyroelectric property is attributed to the morphotopic phase transition between tetragonal and rhombohedral PZT phases in the BT–PZT system. The developed BT–PZT system is capable of generating a power output of 1.3 mW/m2 near the Curie temperature with a constant rate (0.11 K/s) of heating. A signal conditioning circuit has been developed to rectify the time-varying current and voltage signals obtained from the harvester during heating cycles. The output voltage generated by the pyroelectric harvester has been stored in a capacitor for powering wearable electronics.

Temperature Evolution of Physical Properties of BaTi0.9(Nb0.5Yb0.5)0.1O3 Lead-Free Ceramic

BaTi0.9(Nb0.5Yb0.5)0.1O3 lead-free ceramic was prepared by a solid-state reaction method. The structure of BaTi0.9(Nb0.5Yb0.5)0.1O3 has been characterized by means of x-ray diffraction, showing the coexistence of cubic (31.1%) and tetragonal (68.9%) phases at room temperature. Dielectric spectroscopy shows that BaTi0.9(Nb0.5Yb0.5)0.1O3 composition sintered at 1380°C exhibits a relaxor behavior with a weak diffuse phase transition obeying a Lorentz-type quadratic relationship. The ferroelectric–paraelectric phase transition TC decreased from 420 K for BaTiO3 to 284 K for BaTi0.9(Nb0.5Yb0.5)0.1O3. The dielectric loss of this ceramic was <0.09 over a wide temperature range (<400 K). The temperature behavior of the main piezoelectric parameters, such as the piezoelectric coefficient d31 and the electromechanical coupling factor kp, was investigated. d31 sets a maximum about 32.5 pC/N at temperature of 220 K. Nevertheless, kp undergoes more or less important changes between 120 K and 200 K. Over 200 K, kp degrades very rapidly due to the depoling effect deduced from the hysterisis measurements. Dielectric and structural properties of BaTi0.9(Nb0.5Yb0.5)0.1O3 were confirmed by Raman spectroscopy.

Dielectric and electro-optical properties of Mn12-acetate and ferroelectric liquid crystal composite

ABSTRACTThe impact of single-molecule magnet (SMM), Mn12-acetate, on the dielectric properties of ferroelectric liquid crystal (FLC) has been investigated by dielectric spectroscopy and electro-optical techniques in a dual electrode sample cell (DESC). The temperature-dependent dielectric studies on Mn12-acetate/FLC composite have revealed the enhancement in the ferroelectric (smectic C*) to paraelectric (smectic A*) phase transition temperature by 3.5°C. The relaxation process corresponding to Goldstone mode in the ferroelectric phase of the composite is found to be slower compared to pure FLC sample. The electrical response for an input triangular wave shows the existence of one extra polarisation peak in Mn12-acetate/FLC composite which is ascribed to the induced dipole moment in Mn12-acetate molecule. The electro-optical texture of Mn12-acetate/FLC composite revealed that the incorporation of SMM in FLC significantly improve the memory effect.